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I was wondering whether it could be technically and economically sound to put renewable energy plants on rail wagons to deal with the intermittency of the sun and/or wind and/or... or to deal with obstruction issues (like one solar panel shading another when the sun is low on the horizon (PS2) or adjusting the distance between wind turbines depending on the wind speed so as not to put one in the wake zone of the other)? Another advantage could be that one can have production of these power units in one definite location and the logistical aspect thereafter becomes self-explanatory? Transforming the electricity of this mobile power source to a suitable large voltage could be a challenge however? To summarize: does such mobile renewable energy deserve a place in a nice solarpunk scenario?

PS1: I want to emphasize that my question is not about transportation powered by renewable energy, it is about using transportation to improve renewable energy.

PS2: I think that if one has a solar park with densely packed panels mounted on a solar tracking motor, in the mornings and evenings or when the sun is low it is best to rotate some of the panels towards the sun and completely shade the other panels in between. I think so because the general trend with these cells is that the efficiency rises with the intensity of the incoming radiation so that it is always better to rotate some panels to given them the best intensity at the expense of completely shading some of the other panels. I'm ignoring the partial shading problems in this reasoning for a moment.

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    $\begingroup$ (1) One can and does have the production of power units in a handful of definite locations. They are called factories. Or do you think that solar panels and wind turbine blades are manufactured on-site? (2) You are completely ignoring the pesky problem of connecting the generators to the grid. Trust me, for generators of sufficient power to be significant, it is not trivial. (3) Have you tried to fire up Excel or LibreOffice Calc or Google Sheets and try to put together a simplified business case? (4) What does PS2 have to do with the general idea of mobile power plants? $\endgroup$
    – AlexP
    Commented Jan 8, 2023 at 20:03
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    $\begingroup$ I suggezt you watch or read Snowpiercer (I like the movie better than the TV series). It's about a train that never stops, and is able to maintain a population inside. It is powered by hydrogen extracted from snow. $\endgroup$ Commented Jan 8, 2023 at 20:48
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    $\begingroup$ @AlexP: firstly, your comment, while not impolite, sounds agitated... why? Does my post harm anyone? Can't we all chill out and have a little fun? I'll answer to your question number (4): for some large solar panel park, I was thinking about a method to spread out the adjacent panels when the sun is low and compress them again when the sun is high, to avoid shading and have all panels pointed to the sun all time. Why then not put them farther apart all of the time, you ask? Maybe you want to use the territory/infrastructure for other purposes some of the time? $\endgroup$
    – 5th decile
    Commented Jan 8, 2023 at 20:59
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    $\begingroup$ @Bartors: read my PS1 $\endgroup$
    – 5th decile
    Commented Jan 10, 2023 at 11:49
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    $\begingroup$ Note that it is usually not economical to use that 'solar tracking motor'. If you know that it's too costly to slowly rotate the panel in the right direction then I think you have an answer to your question. $\endgroup$
    – ciamej
    Commented Jan 10, 2023 at 16:20

8 Answers 8

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Here is an idea for you. Your planet is hot, not very but hot. Humanity is living close to polar regions and migrate twice a year. Now since everyone is close to arctic, it is meaningful to have power generation closer. Now also imagine close to the poles you have no icesheet, just open ocean.

At latitude 88 degrees, you need to travel about 60km/h (~30km/h at 89) to face noon sun. Normally, without this movement you will get 1/3 of what you will obtain in equator year around but since it is always facing the noon sun, it will be more than doubled.

The amount of production is zero during winters due to 6m of night. But your people migrate in their airships to the other pole, further doubling the output. Thus in total, you will produce about 40% higher amount of energy with this strategy instead of losing 1/3. Obviously you need some power for the movement but it will not be huge as moving a ship at 60km/h does not require a lot of power. Overall a realistic result will be %25 extra power generation and the movement is mandatory for this scenario work. On the flip side you will need twice as many panels.

More: Here is another fun idea

PV's will be on mobile islands. People will also live on these islands. Imagine steampunk mega ironclads moving around the equator. They will have houses, gardens on top of these massive mobile cities. Every house roof will be covered with PV cells. There will be many airship docking stations where people will use them to move to land to collect resources. At the end of the artic day, they will hop on to the same airships and will migrate to the other pole. Also mobile cities will stop moving. There could be some emergency wind power generators while the city is empty.

You could even have some sort of rogue people moving in after the high society leaves the city. They stay there in during the winter will leave without a trace before the spring. Sometimes some items will be displaced and there will be rumors...

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  • $\begingroup$ Something with "balloons made of thin-film PV going from pole to pole" is of course an epic idea (also expressed by Darrel Hoffmann in the comments). Other than that, I don't know what that $1/3$ in your answer is doing. At some point you say my energy gain is going to be doubled at least (compared to the same PV on the equator) but then you say I only win 40%... I think you were more on the money with the former statement. Finally, my people deflate their PV-balloons and take them with them on their journey to the other pole so I don't need to double the area of PV required. $\endgroup$
    – 5th decile
    Commented Jan 10, 2023 at 22:10
  • $\begingroup$ Point of subtlety is that if my balloons are spherical and PV all around there is of course a factor of 4 in waste, but we can assume my people manage to make a kind of polyhedral-shaped balloons with only the relevant face of the polyhedra made in PV. $\endgroup$
    – 5th decile
    Commented Jan 10, 2023 at 22:12
  • $\begingroup$ The central motivation for using PV on balloons is to circumvent the atmospheric scattering, which at the poles has always already chipped away a lot of the solar radiation before it reaches ground level. $\endgroup$
    – 5th decile
    Commented Jan 10, 2023 at 22:22
  • $\begingroup$ I agree with your idea of moving the ships that anchor the balloons with the daytime (so that I get a vertical wall of balloons always facing toward the sun). I checked your calculation about the speed requirement and it seems correct. If I have a wall from 89° to 89° it is already a staggering 220 km long, so that enough for me I think (which means that I can settle for an easily manageable speed of 30 km/h or less for my anchor-ships) $\endgroup$
    – 5th decile
    Commented Jan 10, 2023 at 22:39
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    $\begingroup$ You will have net gain if you move from pole to pole. Used a solar database (renewables.ninja) with the exact coordinates to obtain the values. You get 22% in places close to equator while getting 7% at 88º. This also includes negative effect of temperature (high temperatures is not good for PV) and average cloud cover. Highest value I could find was 22.5. Rest of the calculation is given above. $\endgroup$ Commented Jan 14, 2023 at 15:10
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This would only make any sense if the renewable energy plants were extraordinarily expensive. Think about it - you can either have one power station that you transport all over the place, or you can just build a few power stations in the places you'd be transporting the one anyway. Even if you get a net positive energy gain from transporting a single power station (and that is a very big if), you'd likely have a bigger gain just by having a second station.

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  • $\begingroup$ Note that we already have the necessary rails... Maybe no need to pay for them a 2nd time. The rail could also make the logistics of installation/construction/maintenance relatively trivial and cheap. $\endgroup$
    – 5th decile
    Commented Jan 8, 2023 at 19:59
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    $\begingroup$ @ThibautDemaerel: We definitely do not "already have the necessary rails". Disassembling a wind turbine, loading the parts onto railroad cars, unloading them, and re-assembling the wind turbine is an exercise which takes many days, even assuming that at the destination you already have the concrete foundation ready. In practical reality, shipping the blades of wind turbines calls for a lot of planning. $\endgroup$
    – AlexP
    Commented Jan 8, 2023 at 20:07
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    $\begingroup$ @Vergilius the railes we already have connect different cities, etc. and aren't focused on moving power plants in locations where they're most reasonable to use for a certain time $\endgroup$
    – Jimmy T.
    Commented Jan 9, 2023 at 10:27
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    $\begingroup$ @Vergilius While it might seem like there's a lot of empty rails in a yard most of the time, when a train needs to be assembled, a lot of those empty rails will be needed for that purpose. There's a reason the yards are that big. They haven't just laid a bunch of unnecessary tracks. $\endgroup$
    – Dnomyar96
    Commented Jan 9, 2023 at 13:50
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    $\begingroup$ Tracks between cities are sized and laid out with the premise that trains will follow a predictable schedule and there won't be one huge train careening back and forth willy-nilly. $\endgroup$
    – Cadence
    Commented Jan 9, 2023 at 21:58
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Some quick reasoning for whether this is even theoretically viable using solar:

At most, moving around a panel could take it from 0% output to 100% output.

Current solar panels are about 25% efficient. So the theoretical maximum output for them is ~25 Watts / square foot. Current solar panels weigh something like 2-3 pounds per square foot.

So how much of a panel's output would be needed just to move itself?


Using these estimates for container ship efficiency:

https://www.researchgate.net/figure/Energy-consumption-per-tonne-km-for-a-few-examples-of-ships_fig1_296561654

enter image description here

Let's go with 0.05 KWh to move 1 ton 1km.


So putting things in equivalent units (and doing a lot of simplifying):

1000 square-feet of solar panels weighs 1000kg. It can output, at most, 25 KiloWatts.

So that's 25 KWh per hour, and transporting it via maximally efficient container ship uses ~0.05KWh per km and you might reasonably get 40 km/h so that's 2KWh per hour.


So now the question is:

Could moving a solar panel array around the ocean at 40km/h conceivably increase output by 10% of its potential maximum?

I doubt it.

The solar Terminator moves across the earth's surface at approximately 1,600km/h. This would be 2.5% of that.

Typical clouds move at anywhere from 50 to 200 km/h. So you might be able to avoid/get out of the way of some clouds but your mileage will vary.

And all of this is being very generous with assumptions about the energy cost of moving the panels around (the numbers only work for panels stacked in shipping containers, not actually deployed).

Plus it includes none of the overhead/depreciation costs for the machinery needed to transport the panels and store the energy until it can be connected to the grid.


I think the numbers are close enough that this be plausible for a work of fiction. But definitely not a viable idea for the real world.

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  • $\begingroup$ Thx, you put some real work into your answer. My ship could perhaps serve as an anchor for some big hydrogen-filled balloons coated with some of these thin-film pv they keep talking about? $\endgroup$
    – 5th decile
    Commented Jan 9, 2023 at 13:56
  • $\begingroup$ Also consider what a calm journey during the night informed by next day's weather forecast might do for you. $\endgroup$
    – 5th decile
    Commented Jan 9, 2023 at 14:04
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    $\begingroup$ @Vergilius - if you focus on the right spectrum, clouds are kind of irrelevant, so wouldn't it make more sense to do that rather than waste energy dodging clouds? $\endgroup$
    – jdunlop
    Commented Jan 10, 2023 at 18:40
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A solar panel generates no power at night - spending 50% of it's life doing nothing. If your rail system can move the solar panel so it's always in the sun - while using less than 50% of it's energy output, then the panel on the train is more 'efficient' than one not on a train.

However the equator is big so the train would have to travel 40,000km per day, or 1600kph or about 1.5x the speed of sound.

While it is probably possible, a supersonic train sounds like a big engineering challenge. One that hauls enough solar panels to power itself sounds even harder.


But there is a solution: space. A satelite is above the clouds, above the absorbtion of the atmosphere and ... spends a higher percentage of time not in night (the higher your orbit, the more sunlight you have compared to shade). But then you've got to get that power to Earth - maybe lasers? If the orbit is high enough, you can have your satelite in full sun shining it's laser at a ground-side-collector in the middle of night. (At this point the military swings by and reminds you that your new power system is also an incredible weapon).

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    $\begingroup$ In stead of trying to dodge the day-night cycle, let's start by trying to dodge some cloud formations etc. ;) $\endgroup$
    – 5th decile
    Commented Jan 8, 2023 at 19:45
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    $\begingroup$ Kim Stanley Robinson worked out that this kind of train is viable on Mercury, where the sun heating and cooling the rails was enough to both move the train and provide power. See “Red Mars” trilogy. Bonus: no oceans! $\endgroup$
    – SRM
    Commented Jan 8, 2023 at 22:03
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    $\begingroup$ @Vergilius Why? By the time you get the solar plant broken down, put on the train, driven to its new position, unloaded, and set up, the clouds will have moved or dissipated, and new ones formed. Given the relative speeds of stormclouds (pretty zippy) and trains (not), you're better off just staying put. $\endgroup$
    – Cadence
    Commented Jan 9, 2023 at 8:44
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    $\begingroup$ @Cadence The idea (if I got this right) is not to break down, transport and set up an otherwise static solar plant, but to build it entirely on a rail car, so that it can be moved about without the associated steps. $\endgroup$
    – zovits
    Commented Jan 9, 2023 at 9:38
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    $\begingroup$ You could increase the train's access to sunlight by having it travel a smaller circle up in the sub-Arctic for half the year, and then traveling down to another circle in the sub-Antarctic for the remainder, staying wherever it's summer to have the most daylight. That way it doesn't have to travel nearly as fast to keep up with the rotation of the Earth... Batteries can make up for the brief periods of darkness it might deal with on those transition runs. $\endgroup$ Commented Jan 9, 2023 at 16:02
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There is an Australian Solar Powered Train

As the article suggests, this is a short, level track with one slow train, also charged from panels on the roof of the stations at either end, in a place of high sunshine. It is just viable under nearly ideal conditions.

Sailing ships use renewable energy. There are modern designs such as the OceanBird. These could also carry solar cells and some storage to make getting in and out of port easier.

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    $\begingroup$ I was actually going to suggest something like this - don't power the train. Power the tracks. Put a 3rd rail down with power supplied by stationary solar panels all along the route. Sure, it might be cloudy on some parts of the track, but it's unlikely to be cloudy everywhere, so you've always got a source of free electricity for every train on the tracks. (And the proposed system is global, so day/night is taken care of.) The train in that video apparently produces power to spare, and feeds it back into the grid. $\endgroup$ Commented Jan 10, 2023 at 14:52
  • $\begingroup$ That train shows how hard it would be to make a truck work on solar panels. The train runs on a straight and level track, so it probably consumes no more power than a small truck. There has even been an experiment to add pantograph electricity to the slow lane of a motorway in Gemrmany. I did look at whether I could power a camper van from wind power, so I could tour the UK on found energy. $\endgroup$ Commented Jan 10, 2023 at 20:17
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You can have a mobile solar power supply as a special logistics vehicle if you want that for your story. Just mount a bunch of solar panels on a truck. You can drive the thing wherever you need the power then you have a mobile power supply from renewable sources.

The big issue is efficiency. With current day solar panels the surface area of a typical truck generates nowhere near enough power to move the truck. So it would have to charge for a whole day and then can drive at most a few hours (maybe minutes, I didn't do the math). In a scifi setting you can of course improve the efficiency so this is not an issue anymore.

Alternatively you can say that in power generation mode (when the vehicle is parked) you just unload a whole bunch of solar panels so the area of the panels is much bigger than the surface of the truck.

Note that this seems most sensible for some kind of all terrain vehicle to generate power in remote hard-to-reach locations. If a place has a connection by rail it usually also has a connection to the electricity grid so you don't need to generate your power locally.

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    $\begingroup$ I'm not sure you could increase the efficiency of a solar-powered truck that much. There's a certain amount of energy that sunlight holds, and a certain energy it takes to move the truck, and you can't really change that. $\endgroup$
    – Cadence
    Commented Jan 9, 2023 at 8:47
  • $\begingroup$ @Cadence First question is how hard-science you want to be, your caveat is true but maybe OP doesn't care about that. Second, moving a vehicle horizontally is essentially just overcoming friction, so at least theoretically one could reduce the amount of energy required to drive a vehicle by quite a lot. $\endgroup$
    – quarague
    Commented Jan 9, 2023 at 8:51
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    $\begingroup$ The Carnot efficiency for solar radiation (5800 K) incident on a 300K surface is a staggering 94%. In an infinite-junction architecture, the limit would be 86%. Since the gross incoming power is roughly 1000 W/m^2, a solar system could generate up to 800 W/m^2 (today's best panels do 250 W/m^2). This will probably still not suffice to get a truck moving (while keeping the shape of the truck aerodynamic enough). I already emphasized that my question is not about transportation powered by renewables. $\endgroup$
    – 5th decile
    Commented Jan 9, 2023 at 11:02
  • $\begingroup$ @user253751 : I don't completely understand you, but the premise of my calculation was about powering a truck going at a 'practical' speed (say at least 50 kph) with panels that have to be attached to the truck and cannot increase its aerodynamic drag and have to provide the power required to overcome the drag instantaneously (without any battery backup). Of course, to get something moving at all typically requires much less power. (In practice, trucks have around 500 hp engines according to google) $\endgroup$
    – 5th decile
    Commented Jan 9, 2023 at 11:51
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    $\begingroup$ This is close to my scheme so upvote and mine becomes this comment. The scenario is no grid. The power generators go from isolated place to place, accompanied by a feral kid and the last of the V8 Interceptors. Once in place they go to work. The power generators do. Maybe the kid also. The energy is stored as desalinated water in towers. That water lasts until next time the generators come back. $\endgroup$
    – Willk
    Commented Jan 9, 2023 at 22:01
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I was wondering whether it could be technically and economically sound to put renewable energy plants on rail

Imma stop you right there. No, it couldn't be economically sound to put power sources on rail.

The reason is simple: renewable power sources like wind turbines or solar panels can be scaled down very conveniently to each individual building. And the up side is that saves you a lot of power transmission infrastructure because the power is made where it is consumed.

If you put all that on a train, you have to add the cost of trains with theirs tracks and support infrastructure to build and maintain, and then you have to bring that power from wherever your train is, all the way to your cities. That is a lot of money.

But isn't it worth it if it somehow makes your intermittent sources continuous?

Probably not.

The reality of any power grid is that, as all things should be, it must be perfectly balanced. That means at all times you want production to equal consumption. Not enough power is bad, but too much power is arguably worse. Your power grid needs a way to offload excess energy.

You could waste it into the aether, but it's more sensible to have a storage solution. You can spin a big hunk of metal, pump water up a mountain, heat up some salt, brew some hydrogen fuel, etc.

Your train system would still need to deal with excess energy. By storing it, you also alleviate the problem of intermittent power supply, and that makes the whole train thing redundant.

You also have to consider your train would be a single point of failure, and stopping a train is trivial. It would be a lot harder to lose power if you had panels on every roof.


On water? Worse. Because you have much of the same problems than with a train, but then you also have to bring all that power to land first.

In the air? Even worse. Because floating in the sky indefinitely is a lot harder than floating on water indefinitely, which is also a lot harder than just being on the ground indefinitely. And you still have to transmit power to the ground, which is still presumably where the people live.


You could conceivably use a train as a way to store energy though. You could use excess energy to send a train up a mountain. And then, when you need energy, you let it run down the mountain, recover some energy out of it. It's something we already do, but with water rather than trains.

Would it be more sensible than pumped-hydro storage? Probably not. But it would be more a more sensible use than as a roaming solar panel.

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Basics (Fermi estimate): you can harvest on the order of 100 W/m^2 from sunlight. One rail car is 25 m long, 4 m high, so it produces 10 kW (peak power). A locomotive uses 4000 kW to move 60 rail cars at normal rail speeds (100 km/h), i.e. you're drawing more power than the train generates (600 kW peak).

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    $\begingroup$ Modern panels can do 250 W/m^2 and with CSP and multijunction techniques, 500W/m^2 could be in reach with current technologies. The train cart might be top-heavy since those panels are quite light, so the imagination need not be limited by the measurements of the train cart that you're giving. $\endgroup$
    – 5th decile
    Commented Jan 9, 2023 at 10:19
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    $\begingroup$ You can't make railcars much larger while retaining the ability to use existing rail networks. You'd have to build retractable/folding structures if you want more solar panel area per rail car. $\endgroup$
    – Hobbes
    Commented Jan 9, 2023 at 12:08
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    $\begingroup$ @Vergilius well even at 500W/m2 (seems high), the solar panels will generate 3MW, while the locomotive uses 4MW. Shifting the power plant around only makes sense when the improvement due to displacement is larger than the train's consumption, but we end up that even in an ideal scenario (panels perpendicular to incoming radiation, at hi noon ..etc ) the train eats more than the panels provide. If you want to make this viable, earth must be different: higher solar constant, and super slow dark clouds to make it worth slowly moving away from them $\endgroup$
    – Apfelsaft
    Commented Jan 10, 2023 at 10:12

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